Environmental effects

Invasive marine pests can cause a number of negative environmental impacts. They often compete with native species for space and food, and some introduced species appear to be more aggressive competitors than native ones. By smothering areas of seafloor, some pests fundamentally change habitats. 2631  The following table provides a summary of some of the key impacts from particular species (adapted from MPI’s New-Zealand’s Marine Pest Identification Guide, 2015 2632 ).


Status in New Zealand


Clubbed tunicate/ Leathery sea squirt

Styela clava


  • Fast growing and forms dense groups
  • Filter feeder that competes with native and aquaculture species for food (planktonic larvae) and space
  • Nuisance fouler of vessels, aquaculture and fishing equipment and other artificial structures

Mediterranean fanworm

Sabella spallanzanii


  • Forms dense groups
  • Competes with native species for food and space
  • Negative impact on the establishment of new generations of some species, and on nutrient flow in the water column
  • Dense beds foul fishing equipment and aquaculture structures

Japanese kelp

Undaria pinnatifida


  • Rapidly forms dense stands that overgrow and exclude native seaweed species
  • Nuisance fouling causes problems and increased costs  for aquaculture

Asian paddle crab

Charybdis japonica


  • Aggressive crab that can out-compete native crabs for space and food
  • Threat to aquaculture as it preys on shellfish
  • Carries White Spot Syndrome virus which can infect native and farmed prawns, crabs and lobsters


Pyura doppelgaengera (previously P. praeputialis)


  • Forms dense populations or mats, and can survive in a wide geographical range
  • Could displace important native New Zealand species, including green-lipped mussels

Australian droplet truncate

Eudistoma elongatum

Previously detected, not established in the environment

  • Quickly spreads and smothers other algae, seagrasses and invertebrate communities
  • Out-competes native species for food or light and produces toxic compounds
  • Vast beds can destroy native species diversity and fish habitat
  • Tangles in nets and anchors
  • If aquarium Caulerpa was to escape into the marine environment, there is a high risk of it establishing and severely damaging the marine environment

Asian clam

Potamocorbula amurensis

Not Detected

  • Reduces planktonic food sources, causing decline in abundance and diversity of native species, and decline or collapse of commercial fisheries and farmed shellfish
  • Reaches extremely high population densities, altering the soft sediment community structure of an area by changing the sediment structure, and reducing the space available for other species

Chinese mitten crab

Eriocheir sinensis

Not Detected

  • Burrowing weakens banks and causes accelerated erosion
  • Hosts liver fluke (Paragonimus sp.) that is harmful to human health
  • Consumes both plants and animals

European shore crab

Carcinus maenas

Not Detected

  • Highly adaptable invasive species
  • Voracious predator – eats mussels, crabs, oysters, limpets, barnacles, worms, juvenile crabs and shellfish, including scallops
  • Potential to significantly alter ecosystems causing mortality in native crab and shellfish populations
  • Implicated in decline of native shellfish populations overseas, some of commercial importance

Northern Pacific seastar

Asterias amurensis

Not Detected

  • Voracious predator of native species and economically important farmed shellfish
  • Potentially serious impacts on aquaculture, fisheries and wild shellfish populations

Last updated at 1:40PM on February 6, 2018